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In this paper, an overview of MANET, Routing Protocols and the application areas of MANET are provided. Broad categories of routing protocols used in MANETs such as PRP,RRP,HRP are discussed in brief. There is trade off in both and PRP and RRP to update the routing table frequently or immediate route discovery when needed. The size of the network and the frequency of the change in topology are the key factors that affect the choice of the protocols.
A Mobile ad-hoc network is the set of wireless mobile devices dynamically forming a temporary network without the use of any existing network infrastructure. Mobile ad hoc networks are popularly called as MANET. MANETs are dynamic and independent of any fixed infrastructure and networks topology may change frequently. This gives the MANETs two of its most desirable characteristics adaptable and easy to deploy.
The main functionality of the MANET is that it can be used where the deployment of a wired network is impossible. MANETs are more innovative and challenging technology to the wireless ad-hoc networking technology.
MANETs employ the traditional TCP/IP structure to provide end-to-end communication between nodes. However, due to their mobility and the limited resource in wireless networks each layer in the TCP/IP model require redefinition or modifications to function efficiently in MANETs. (REF)
MANETs are standalone wireless networks. Traditional cellular networks are still limited as they have major limitations when compared with MANET. The Limitations of the cellular network over the MANET can be discussed: They can be tabulated as follows:
Infrastructure is required to deploy the networks
Speed of deployment is fast as it is impendent of any pre infrastructure
Static network topology
Network topology is highly dynamic as the mobile nodes are moving frequently
Needs clear planning in case of new installation or any changes.
Easily adaptable in case of any changes
Large set up time and cost
Cost effective and less set up time
1.1 CHALLENGES OF MANET:
Limited wireless transmission range.
Highly Dynamic and frequent changes in Topology
Hidden terminal problem
MANETs based on wireless links; significantly have lower capacity than wired networks.
MANETs are affected by higher loss rates and higher delays due to wireless transmission.
MANET nodes rely on batteries. So energy saving is an important criteria in the system design.
Potentially frequent network partition
Security is limited due to the wireless transmission
There is no centralized control for MANETs.
2.0 ROUTING AND MOBILITY MANAGEMENT IN MANETs:
In MANETs with dynamic infrastructure, as communicating devices is frequently moving freely there will be change of routing paths. So to form a MANET device must keep track of the each device locations and interconnectivity as they move. Routing is the challenging area in MANET.
In this context, mobility management in MANETs involves three Mechanisms - route discovery, route selection and route maintenance.
Route discovery To send the traffic from source to destination the source node needs to know the route to the destination node. Initially it will check whether the routes are readily available or not. If so, source node will use the route to send the traffic. On the other hand, if the route to source to destination does not exist then it will initiate the route discovery process. To find out the route source node uses flooding mechanism in which a query packet is broadcasted throughout the entire network. When the query packet is received by destination, a reply packet is sent back to the source, indicating the route to the destination. Then reply packet will travels in reverse direction to reach the source node.
Route selection selecting an optimal route or path among the available routes from source to destination is the tedious task. So there are many metrics considered for selecting an optimal route. In case of MANETs mainly shortest path is the main metrics as the devices are frequently moving.
Route Maintenance it is the mechanism, which keeps track of whether the network topology has changed and decides whether the route reconstruction is required or not.
3.0 MANET PROTOCOLS:
As the MANETs is highly dynamic adding complexity to routing among the mobile nodes. To accommodate the changing topology special routing protocols are needed. And as there are limited resources in the MANET, designing and implementing an efficient routing protocol is a challenging task. These protocols used in MANETs can be broadly classified as
Proactive or Global Routing Protocol (RRP)
Reactive or On demand Routing Protocol (PRP)
Hybrid Routing Protocol (HRP)
3.1 PROACTIVE ROUTING PROTOCOL:
In proactive routing protocol each node in MANET will evaluates all possible routes to all reachable destinations independently of the traffic pattern. Traditional wired network uses proactive protocols. Separate routing table is constructed and maintained and it contains list of possible destinations, number of intermediate devices to reach each destination and the information about the next node. When a network topology changes, change needs to be updated in all nodes and needs to be communicated throughout the network. PRP is also called as table driven routing. This proactive routing uses connection less protocol approach.
3.1.1 ADVANTAGES AND LIMITATIONS OF PRP:
The main advantage of using proactive routing protocols is that, when a node needs to send the data, it can send the data immediately without any delay as the routing information is readily available. Delay of Route discovery is avoided here.
As the routes are maintained at all the time, Latency of route discovery is very low.PRP provides higher overhead in route discovery and route maintenance as the routes are continuously getting updated. Each node updates and maintains all routes regardless of the usage of the route. Also maintains a route between a source and destination even if the source never requires that path.
3.1.2 DIFFERENT PRP IN USE:
Most proactive routing protocols inherited the properties from the algorithms used traditional wired network. However to adapt the key feature of MANET i.e. dynamic nature necessary modifications have been made. Some of the protocols used in MANETs are:
WRP - Wireless routing protocol
DSDV - Destination-Sequenced Distance Vector
OLSR - Optimized Link State Routing
FSR - Fisheye State Routing
HSR - Hierarchical State Routing
TBRF - Topology Broadcast Reverse Forwarding.
3.2 REACTIVE ROUTING PROTOCOL:
In contrast to the PRP, reactive routing protocols evaluate the network and create routes only when there is a need to send data. It is also called as On-Demand Routing protocols. If there is no traffic then the routing activity will be totally absent. It is like a connected oriented service, however route is not readily available when needed but route can be created through route discovery. Route discovery process is carried out in query-reply basis, in which the data source floods the query packet into the network to discover a route to the destination. On receipt the destination send a reply back to the source. As the copy of query packet travels through the multiple routes destination receives the multiple copies and sends more than one reply to the source through different routes. Source will receive multiple replies from destination from various paths and it decides the optimal route from its own route selection criteria.
3.2.1 ADVANTAGE AND LIMITATIONS OF RRP:
In RRP overhead is very less as the as the route between the source and destination is evaluated and created only when needed. Additional overhead of updating and maintaining the routing tables are eliminated here.
In RRP, latency is very high as the route needs to be identified with the route discovery and route selection process. So there will be delay in processing of data. Because of long route discovery process and lack of route information readily available, reactive protocols may not be applicable in real time communications.
3.2.2 DIFFERENT RRP PROTOCOLS:
Some of the important RRP are listed below
DSR - Dynamic Source Routing
AODV - Ad hoc On-Demand Distance Vector routing protocol
TORA - Temporally Ordered Routing Algorithm
ABR - Assosiativity Based Routing
SSR - Signal Stability Routing
3.3 HYBRID ROUTING PROTOCOL:
Due to the dynamic change in the topology the protocol that works well in one MANET may not work well in another with different resource parameters. RRP are well suited where there are limited traffic and PRP on the other hand suited for the high traffic networks. So, what ideally needed is a single routing protocol that has the capability to adapt the dynamic nature of the MANET. Hybrid routing protocols are new generation protocols which are both proactive and reactive in nature. HRP are proposed to combine merits of both PRP and RRP and overcome their shortcomings. Some of the HRP are
ZRP - Zone Routing Protocol
ZHLS - Zone based Hierarchical Link State
SLURP - Scalable Location Updates Routing Protocol
DST - Distributed Spanning Tree based routing protocol
DDR - Distributed Dynamic Routing protocol
3.3.1 ADVANTAGE AND LIMITATIONS OF HRP:
The advantage of HRP is to adjust its routing strategies according to the network traffic and thus providing an attractive routing in MANETs. However the network natures such as mobility and traffic pattern can be dynamic. Again it is very difficult to discover and maintain the information. This complexity leads to dynamically adjusting routing strategies are hard to implement.
3.4 SUMMARY OF MANET PROTOCOLS:
4. APPLICATION AREAS OF MANET:
Below are the some areas where MANET are used frequently. Mainly used in the scenarios where the wired networks are impossible to use.
Students on Campus
MANETS are seen as a key in the evolution of wireless networks. They have several potentialities that are not available with traditional wireless networks and can be used in different environment where the we need an infrastructure less standalone network is required. Routing is the most challenging area in the development of MANETs. There are number routing of protocols available for MANET. Each protocol provides the different strategies. It is difficult to determine which protocol may perform better in each circumstances.
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HRP uses the features of both PRP and RRP to perform better in large networks. Each protocol has its own advantage and limitations. However still the researches are going on in the routing area of MANET to provide the better performance and to face the new challenges.